Field of the Invention
This invention relates generally to high powered compact electric motors, and more particularly, to a motor and reducer system, the motor being an outer rotor motor that is particularly adaptable for motorized drums used in a conveyor or the like to drive a conveyor belt or the like around the drum shell, and more particularly to sanitary conveyor motorized drum applications. In addition, this invention relates to a sanitation system that monitors fluid pressures within high powered compact electric motors, as well as fluid pressures within conveyor rollers and supporting structures, the sanitation system being particularly adaptable to sanitary conveyor applications.
Description of the Related Art
Motorized drums are predominantly configured so that a motor and reducer are disposed within a drum shell and the rotations of the motor are reduced by the reducer and then transmitted to the drum shell so that when the external shafts are secured to the frame of a conveyor, the drum shell is able to rotate. In some embodiments, the drum shell drives a flat belt, or toothed belt, or modular belt.
The motorized drum that is currently available has a drum shell and the motor and reducer are housed within this drum shell. Bearings and seals are disposed at both end sections of the drum shell with end covers for closing these end sections disposed between the bearings and the drum shell. Labyrinths are frequently used in the end covers to protect the seals from high pressure water that is used to clean food processing plants. There are employed first and second mounting shafts that enable rotation relative to the drum shell. Accordingly, the drum shell rotates about a central axis of the first and second mounting shafts. The first mounting shaft contains a hollow portion through which the motor wiring leads, which are connected to the motor, exit the motorized drum. The known motorized drum is partially filled with oil, which lubricates the open gear box and bearings, and transmits the heat from the motor to the inner periphery of the roller drum as the oil moves throughout the motorized drum.
The known motor has an internal rotor with a shaft attached. This motor rotor shaft also functions as the input shaft for the reducer. The reducer has an output shaft that is coupled to the shell while the fixed reference point of the reducer (it's housing) rotates relative to the drum shell and has no rotary motion relative to the motor stator and mounting shafts. When the motor is energized, the shaft of the known motor rotates. The speed of this rotation is reduced by the reducer, and the reducer output power is then transmitted to the drum shell via the output shaft, thereby driving the drum shell into rotation. In order to achieve smooth operation, the central axis of the motor output shaft and the central axis of the first and second mounting shafts must be in substantial alignment with each other.
The food processing industry is often a twenty four hour cycle that typically employs two shifts of production and one shift of cleaning. The focus is on high throughput, and downtime is not acceptable. Equipment failure must be repairable immediately or replaceable with spare parts.
Existing motorized drums are essentially custom products. Four variables are involved in the selection of a motorized drum. These are: belt speed, belt width, belt pull, and pulley diameter. Additional options may also be included in the analysis, such as lagging, various electrical options, and the need for reinforced shafts.
Currently, the industry predominantly uses AC induction motors that operate at a fixed speed. A motor speed and a gear reduction arrangement must be selected to provide the highest possible belt pull for the application, while creating the lowest amount of heat. The heat issue is critical as the motorized drum is a closed system that renders removal of heat to be very difficult. Therefore a large number of motors, in different poles, must be considered for each diameter along with multiple two and three stage gear boxes.
Currently, the industry uses helical gearing that is limited by the diameter and axial length of the pulley. Therefore, to transmit the necessary torque through the gear box, it is often necessary to use a larger diameter pulley, which is usually not preferred by the market.
In order to have the correct motorized drum available for each application, the manufacturer would need to stock thousands of possibilities, which is not financially feasible. Therefore, each motor is custom built based upon the four variables noted above, resulting in unacceptably long lead times to the industry. As zero downtime is a market requirement, the food processor customer must stock spares of all the motors he uses. This can be as many as several hundreds of motors, requiring high capital investment and cost.
Therefore, it is an object of this invention to create a modular motorized drum that can eliminate the customer's need for a large spare parts inventory by means of a motorized drum produced in its minimal axial length (hereafter, base unit), that includes a mounting face system on one end of the motorized drum onto which various components can be mounted. Such components include end lids, additional extension drum shells and an extension shaft that can accommodate the attachment of sprockets, among others.
It is a further object of this invention to increase the torque density of the motorized drum so that the modular base unit can be a single unit in a preferred diameter and axial length.
It is another object of this invention to provide a motor that maintains a relatively constant torque and efficiency curve across a broad speed range so that a single base unit can be used in all applications within a given production plant.
Customers require spares and spare parts because of the high likelihood of catastrophic failure present in the current art. One contributor to catastrophic failure among current art is the high belt pull and/or tension of the belt on the motorized drum that causes severe and immediate damage to the internal components. Existing motorized drums use segmented or partial shafts. A partial shaft is fixed to the conveyor and enters the motorized drum and is attached to a motor flange. The motor flange is attached to the motor, and the motor is attached to a gear box. The gear box is attached to a partial shaft that exits the motorized drum and is then affixed to the conveyor. These partial shaft segments are either substantially coaxial or are parallel with the motor shaft portion. The dividing of the shaft axially, however, diminishes the transaxial rigidity of the shaft, causing flexure and misalignment between the partial shafts and thus between the motor and transmission.
Such misalignment creates inefficiency, high wear, and often catastrophic failure of the transmission or motor. Prior art efforts to alleviate this problem by include increasing the diameter of the first or second mounting shaft within the motorized drum as the axial length of the motorized drum increases. Others in the art have sought to compensate by using axially longer end lids.
Therefore, it is an object of this invention to accommodate the misalignment between all components of the motorized drum and to accommodate, rather than minimize, the inherent forces causing deflection that enters the motorized drum.
Another significant problem with existing art is its inability to comply fully with the food safety demands of the market. First, it is noted that existing products are filled with oil in order to lubricate gears, bearings, and seals. The oil also transmits heat from the motor core to the shell, where it can be removed by conduction to the belt. Further, system inefficiencies create heat and build pressure in the system, forcing the oil to leak through the rubber lip seals—especially where scoring has occurred in the shaft at the seal. Oil leakage creates the risk of contamination of the food products.
Therefore, it is yet another object of this invention to eliminate the use of oil in the motorized drum.
Second, it is a significant problem with existing motor designs that harborage points exist in the exterior of the drum unit wherein bacterial colonies (i.e., pathogens) can grow. Examples of efforts to alleviate this problem include the use of a labyrinth in the end lid that is used to protect rotary shaft seals from high pressure washing. Also, external bolts and washers are used to connect the end lids to the drum shell, and further bacterial harborage regions are present between the drum shell and its end lids.
Therefore, it is a further object of the invention to eliminate harborage points where colonies of bacteria can flourish.
Third, existing motorized drums that drive modular conveyor belting or toothed driven belting, predominantly engage the belting by means of grooved rubber or polyurethane lagging. This lagging will crack, lift, or pit, thereby not only creating additional harborage points for bacteria, but also serving to isolate heat within the motor. The result is that currently available motors must be derated typically by approximately 18%. This means that more heat is created in relationship to the work performed because the motor is now running at decreased efficiency. The lagging therefore causes the pulley to take a longer period of time to reach steady state, and when it does reach the steady state condition, it does so at a higher temperature than would have been the case without the polymeric lagging, ultimately resulting in higher belt temperature. This additional heat must then be removed from the lagging by the conveyor belt. As the conveyor belt moves along the conveyor, the heat typically is removed from the belt either by convection into the environment or through conduction into the food product being conveyed. It is desired by food industry personnel that no heat from the drive system enter into the food product.
Other prior art arrangements drive modular conveyor belting or toothed driven belting by mounting sprockets to the drum shell instead of lagging. In such arrangements, the conveyor belt does not contact the drum shell directly, and therefore the drum motor still needs to be derated. Further, the sprockets, in their various mounting structures to the shell, create harborage points or dead spaces where bacterial colonies can grow.
Therefore, it is an object of this invention to reduce the steady state temperature of the motorized drum.
It is a further object of the invention to increase the rate of heat dissipation from the windings within the electrical motor to the inner surface of the drum shell.
Fourth, the food industry is concerned about potential cross contamination between the materials within a motorized drum and the food products being conveyed. Thus, the industry continues to seek a solution that will announce the presence of conditions that produce a likelihood of cross contamination. For example, many food industry customers require that red or blue dyes be added to a food grade oil so that when oil leaks, it can be detected. This proposed solution is not reliably effective because after the motorized drum is operated for a period of time, the oil becomes black and the red or blue dye no longer functions as an alert. Additionally, even when there is no actual leakage of oil, cross contamination is still a threat because bacterial colonies will grow in a labyrinth or seal unnoticed, which can then be propelled onto the conveyor during performance of a high pressure cleaning procedure.
Therefore, it is still another object of this invention not only to eliminate the use of oil in a closed system, but also to monitor the corruption of the rotary shaft seals and the static end lid seals in order to alert the system operator in a timely manner that the integrity of the seals has been compromised.